The long-term objectives of this application are to understand the molecular mechanisms which control differential gene expression in oogenesis and early development in Xenopus laevis. Our interests, therefore, are related to basic eukaryotic molecular biology as well as developmental biology. The methodological approach includes standard recombinant DNA technology. In addition, a significant fraction of the research plan consists of the completion and exploitation of a novel method to clone open ready frames (orfs) directly from genomic DNA. This will allow us to score the presence and behavior of "average" mRNAS during oogenesis and embryogenesis. We will utilize these orf clones, more standard cDNA clones (for known and unknown gene products), and in vitro translation to monitor a number of events in oogenesis and early embryogenesis. Specifically, we will measure what fraction of Xenopus genes are transcribed in oocytes, tadpoles, and liver and what fraction of these mRNA are common to all these tissues. We will characterize further the structure of oocyte RNA to search for RNA molecuses stored in non-mRNA (precursor?) form. We will characterize oocyte nuclear RNA to find out which sequences are present in oocyte germination vesicles and in what form. We will also continue to search for any oocyte sequences which accumulate during oogenesis. We will also pursue recent observations that we have made on the molecular events of oocyte maturation and early embryogenesis. These include the adenylation and deadenylation of specific mRNAs as well as the degradation of certain mRNAs. We will also define the relationship of these events to changes in in vivo protein synthesis at these times. An attempt will be made to define and characterize the mRNAs associated with the nuclei of early embryos. Finally, the actin genes of Xenopus will be characterized. Two of these genes will be used in oocyte injections experiments to constitute a homologous Xenopus oocyte injection system which might shed some light on transcriptional control in oocytes. These experiments are of significance to the biology of early development because amphibians are among the only vertebrate systems in which oogenesis and early embryogenesis can be studied biochemically.